I know they can't be added to. What I meant was is it possible to burn a copy of calibre with a library to a CD/DVD so that a readable library is made.

I don't think Calibre will even run without Write access.
If you use a CD/DVD for (backup) Transport: consider zipping the Library FIRST and backing up the Zip. That way, the Read only flag does not get set on any internal (to the Zip) file or folder.

FB Reader Portable runs fine on a USB Flash Drive because the program can write to the Flash Drive.

I just burned it to a DVD to see if it would run.

The good news: Yes, it ran fine, after a popup message saying that the path had changed and it isn't advisable to change the path for a portable program.

The bad news: Without being able to write to disc, the program can't remember the last book you were reading. Furthermore, even if you had only one book on the DVD, it couldn't remember the last page you were reading.